> http://www.karinya.net/g3txq/temp/ground_zones_2.png
Steve,
Do you know if the elevation chart would change much if instead of a
ground-mounted 80m quarter-wave vertical, a half-wave vertical dipole was
used ? The maximum current point would rise a quarter wave above the ground
and the Fresnel geometry would seem to change, albeit slightly in relation
to the horizontal distance.
Paul, W9AC
.
----- Original Message -----
From: "Steve Hunt" <steve@karinya.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Friday, January 07, 2011 9:22 AM
Subject: Re: [TenTec] New and Improved Terminology
> Folk who have been following the discussion may be interested in this
> chart:
>
> http://www.karinya.net/g3txq/temp/ground_zones_2.png
>
> It shows how the optimum take-off angle of an 80m quarter-wave vertical
> mounted over Sandy Soil varies as the radius of an excellent ground
> screen (Salt water) is gradually extended outwards. It was produced by
> using the capability of EZNEC to have two different radial ground media,
> as I described earlier.
>
> Please note that this is simply an exercise in determining how far from
> the antenna, ground conditions affect the take-off angle; we're letting
> EZNEC do the trig that we could otherwise easily do ourselves with some
> simple maths.
>
> Notice that as the ground screen grows from zero to about 100ft - the
> range in which we might typically install a ground radial system - the
> take-off angle barely changes. At the other extreme, above 500ft we are
> beyond the Fresnel Zone in which reflections are taking place, and there
> are no more improvements to be had. All the "action" takes place between
> 100ft and 500ft.
>
> Unfortunately, for many of us that's an area that might well be outside
> our property boundary. Even if it is not, at that radius the areas are
> so great that we would need to put down massive amounts of copper to
> have any significant effect on the ground conductivity. Hence Rudy
> Severn's comment: "Any practical ground system will not affect the
> radiation angle or far-field pattern!"
>
> 73,
> Steve G3TXQ
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